2 Answers
2

Use a vacuum pump. People who pour liquid rubber into moulds use a vacuum chamber to get the bubbles out; I've heard of people degassing wine with a vacuum pump (see these youtube videos, for example); I wouldn't know why it wouldn't work for soup.

The question is of course where you get a vacuum pump. If you're doing this in a commercial kitchen I'm sure there are channels where you can get a professional one. For the home cook (like me), one option (inspired by one of those videos) would be to pour it into a wine bottle and then use a wine saver; Vacu Vin is a well known brand. You probably won't want to fill the bottle more than half full, especially if the liquid is very thick; the bubbles in the liquid will expand a lot if you lower the pressure, and it will raise the level of the liquid.

I'd love for someone to give this a try before I consider such equipment. I was thinking maybe something along the lines of a paint mixer on low setting -jiggle out the bubbles!
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Pat SommerSep 25 '12 at 19:57

With a paint mixer I'd be worried I'd be incorporating bubbles into the soup rather than letting them escape - but who knows, it might work!
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Erik P.Sep 26 '12 at 13:10

Separate the liquid from the solids before blending. Use a fine colander, or coarse sieve

Use a chopper style food processor or a sturdy masher to blend down the solids in a strong bowl, and then add that blend back to the soup. I always leave some extra chunky bits for interesting textures

Blending with a gelatinous liquid (typical of soup) will result in a heavy foam, which may not dissipate for quite some time

Note: In general, most vegetable matter will become softer and breakdown quicker with just cooking if it is in an alkaline liquid. A pinch or two of baking soda may help. e.g. A 1/4 tsp of baking soda will render two onions to mush in about five to ten minutes

Add some neutralising acid (a splash of vinegar or lemon juice), and oily and other acidic components (e.g. tomatoes) near the end of cooking if possible